“Bulk e-mail” refers to large numbers of e-mail messages sent by a single sender to a large number of recipients. Bulk e-mail may either be e-mails that are requested by the recipient, such as a message from an e-commerce website listing their weekly specials, or can be unsolicited bulk e-mail (UBE), more commonly known as “Spam.” UBE and requested bulk e-mail can overwhelm a recipient e-mail system due to the resulting high volume of traffic. Additionally, UBE may include messages that contain computer viruses, scams, or other unwanted and undesirable content.
UBE can typically be removed before it reaches an individual recipient's inbox using content filters, more commonly known as Spam filters. Content filters scan the text of an incoming e-mail message to determine whether it includes offending content which may be indicative of UBE. However, scanning each incoming message for specific content is very resource intensive. While content filtering can reduce the amount of traffic behind the frontline, or the first servers to receive an incoming transmission, the frontline server must expend vast system resources to scan all incoming messages for offending content. Another disadvantage of content filtering is that it is possible that content filters may inadvertently reject messages that an e-mail recipient wishes to receive. Messages that are unintentionally removed with a content filter are known as “false positives”, which are obviously undesirable since an e-mail recipient may not receive an important message based on its' content.
Other schemes for preventing the delivery of UBE exist. For example, realtime black lists (RBL) can cause an e-mail recipient server to perform a domain name system (DNS) lookup to a DNS server that contains a list of UBE senders. The recipient system can then compare an address of the sender with addresses on the RBL. RBLs still require an extra lookup step, which consumes the recipient's resources, and can reduce server responsiveness.
Bulk e-mail of any type can overwhelm a recipient system because of the large number of e-mails that are received at one time. For example, an airline sending out its list of monthly specials may send those e-mails all at once. If a recipient e-mail system has a number of subscribers to this monthly message, the system may become overwhelmed when the e-mails arrive. The receiving system may be overwhelmed not only because of the incoming bulk e-mails, but also because of otherwise normal activity. For example, the highest periods of activity on e-mail systems tends to occur during the day. If a bulk e-mailer were to send a number of messages to a corporate e-mail server at 3:00 p.m., during business hours, the e-mail system may be concurrently handling voluminous amounts of other e-mail traffic. The addition of the bulk e-mails at that time may overwhelm the system, requiring the e-mail server to be upgraded at considerable expense.
Another way to limit the amount of incoming traffic is to limit the rate of messages incoming from specific known bulk senders. For example, each bulk sender has an Internet Protocol (IP) address that identifies the server from which the e-mail is being sent. An e-mail recipient server can have a preset rate limit for each sender based on their IP address. The limit may be expressed in terms of the amount of data per second, the number of messages per second, etc. These rate-limiting techniques may also form part of a larger “abuse” rating. An abuse rating measures the amount of abuse inflicted upon the recipient server by a certain IP address. The abuse rating may also include several other factors, such as the type of message, the typical size of the messages, or the number of messages.
The abuse rating may effectively limit the amount of bulk e-mail received by a recipient e-mail server. However, for various reasons, the recipient e-mail server operator may want to receive certain messages being sent by certain senders. However, these messages might still overwhelm the system if they are sent during peak times. What is needed is a method for limiting bulk e-mails at certain times in order to even out the e-mail traffic on a specific e-mail server.